1. Field of the Invention
The present invention relates to manufacturing of a semiconductor device, and more particularly, forming of a thin film such as a dielectric film in a capacitor.
2. Description of the Related Art
The capacitance (C) of a capacitor is proportional to the area (A) of the capacitor's electrodes and a dielectric constant (∈) of a dielectric material between the electrodes, and inversely proportional to distance (d) between the electrodes, as shown in the following equation.C∝ε(A/d)
Thus, increasing the area (A) of electrodes, using a dielectric film having a high dielectric constant, or decreasing the distance between the electrodes can increase the capacitance (C) of the capacitor.
As semiconductor devices become more highly integrated, the areas available for capacitor formation within semiconductor devices become smaller. Accordingly, techniques have been developed for increasing the capacitance of capacitors formed in small areas. One technique uses three-dimensional electrodes to increase the area (A) of the electrodes, but the three-dimensional electrodes are subject to structural restrictions. Use of a dielectric film having a high dielectric constant (ε) can increase the capacitance (C) of a capacitor and permit high semiconductor integration. In addition, a thinner dielectric film reduces the distance (d) between electrodes and produces higher capacitance of a capacitor, but reducing the distance (d) between the electrodes often has the drawback of increasing the leakage current of the capacitor.
Recently, tantalum oxides, such as a tantalum pentoxide (Ta2O5) having a high dielectric constant (ε), have been tried as dielectric films for capacitors. However, with a tantalum pentoxide film, leakage current can be large when the film is thin. A problem with tantalum pentoxide is non-uniform film deposition, and oxygen and carbon impurities often allow the leakage current through weak portions of the tantalum pentoxide film. To solve the leakage problem, several methods have been suggested. Among the suggested methods is a dry-oxygen (dry-O2) annealing, and a low temperature ultraviolet-ozone (UV-O3) annealing at 500° C. or less followed by a dry-oxygen annealing. IEEE Transactions on Electron Devices, Vol. 38, No. 3, March 1991, entitled “UV-O3 and Dry-O2: Two-Step Annealed Chemical Vapor Deposited Ta2O5 Films for Storage Dielectrics of 64-MB DRAM's”, by Shinriki and Masayuki Nakata, which is hereby incorporated by reference in its entirety, discloses the latter method. In the known methods, formation and UV-O3 annealing of the tantalum oxide film are respectively performed in separate chambers shown in FIGS. 1 and 2.
Referring to FIG. 1, a chamber 8 for forming a tantalum oxide film includes a shower head 10 in an upper portion of chamber 8. Shower head 10 receives pentaethoxytantalum as a source gas for the tantalum oxide film from a supply line 12 and oxygen (O2) as a reaction gas from a second gas supply line 14. A first valve 12a and a second valve 14a are in the first and second gas supply lines 12 and 14, respectively. A susceptor 16 is on the floor of the chamber 8 for mounting of a wafer 18. A pumping line 20 connects to the bottom of the chamber 8, and a pump 22 attaches to the pumping line 20. After forming the tantalum oxide film, wafer 18 becomes a wafer 23, which is transferred to an annealing chamber 9 (FIG. 2). In annealing chamber 9, a UV-O3 annealing is performed on the tantalum oxide film.
Referring to FIG. 2, UV-annealing chamber 9 includes a quartz window 11 on the ceiling thereof. A UV lamp housing 13 includes a UV lamp 15 for generating UV rays that pass through quartz window 11 into chamber 9. A shower head 17 below quartz window 11 is also made of quartz to uniformly pass UV rays into chamber 9. Shower head 17 supplies a gas mixture containing oxygen (O2) and ozone (O3) gases that form an oxide film with a uniform thickness. Shower head 17 connects to an ozonizer 19 installed outside chamber 9. A susceptor 21 is on the floor of chamber 9 and below shower head 17, and wafer 23 having the tantalum oxide film is on susceptor 21. An ozone decomposer 25 connects to a bottom of chamber 9 via a pumping line 27, and a pump 29 connects to ozone decomposer 25.
As described above, the conventional method forms a tantalum oxide film and uses a separate chamber for a UV-annealing to remove defects from the tantalum oxide film.